1. Field of the Invention
The invention relates generally to integrated circuits and more particularly to a single chip RF integrated circuit GPS downconverter having a standby mode controlled by a power supply input used as a logic signal.
2. Description of the Prior Art
Global Positioning System (GPS) receivers determine location, velocity, and time by receiving and processing information in GPS signals received from GPS satellites that have been placed in orbit around the Earth by the United States Government. Each GPS satellite uses a distinct pseudo-random noise (prn) code for spreading data for the location-in-space and time-of-transmission for that satellite and transmits the spread data on a carrier frequency that is the same for all the satellites. A GPS receiver uses the distinct prn code for distinguishing the GPS signal from typically at least four satellites and then finds its own location, velocity, and time by solving simultaneous equations using the relative times that the signal from each of the satellites arrives at the receiver and the locations-in-space and times-of transmission from the satellites.
There is a need for improving the state-of-the-art of GPS receivers in terms of reducing their size, power consumption, and cost. One of the major components in determining the size, power, and cost in the GPS receiver is the radio frequency (RF) circuitry at the front end for downconverting the GPS satellite carrier frequency to an intermediate or baseband frequency. A second major factor is the digital signal processor (DSP) circuitry for processing the signal at the intermediate or baseband frequency for providing GPS signal correlations. Due to the relatively high frequency of the GPS satellite signal, most GPS receivers until recently have used discrete components for the front end RF circuitry. Although the performance of such RF circuitry may be very good, these discrete components represent a large portion of the size, power, and cost of a modern GPS receiver. Gallium Arsenide (GaAs) integrated circuits (IC)s have been developed using field effect transistors (FET)s as active devices for replacing the majority of the discrete components in the RF circuitry. Unfortunately, GaAs ICs have been and continue to be relatively expensive because the commercial manufacturing volume of GaAs ICs is low and because the GaAs material is more expensive than Silicon and the processing steps in manufacturing a GaAs IC are relatively difficult. Silicon bipolar ICs using bipolar transistors as active devices have been used for the front end RF circuitry in the GPS receiver. Such ICs can be more difficult to design because the frequency response, noise figure, and power consumption for the silicon IC bipolar transistors are typically not as good as for the GaAs IC FETs. However, the silicon bipolar ICs are less costly and have recently been shown to have sufficient performance for most applications. There continues to be a need for improvements in RF ICs in order to improve performance and reduce size, power consumption, and cost in a GPS receiver.
The size and power consumption of both the DSP and the RF integrated circuits can be reduced by using improvements in the manufacturing processes for fabricating and packaging silicon chips. Power consumption is further effectively reduced by having a standby mode in which some or all of the circuits are turned off. Over a given period of time the GPS receiver will spend some time operating normally and some time in the standby mode so the effective power consumption is the time weighted average of the standby and normal modes. However, a limiting factor on the size of both the RF and the DSP integrated circuits is the number of pins that are required for supplying power and clocks and passing signals in and out of the chips. Typically, several separate power pins are required for the RF IC in order to prevent unwanted signal coupling between circuits within the RF IC, several clock signals are passed back and forth between the RF IC and the DSP IC, and at least one separate pin is used for controlling the standby mode. It would be desirable to reduce the pin count in one or both of the RF IC and DSP IC by having multiple functions performed through a single pin.